我希望“剪切”div的左上角,就好像你已经折叠了一个页面的一角。
我想用纯CSS做,有什么方法吗?
答案 0 :(得分:89)
如果父元素具有纯色背景,则可以使用伪元素来创建效果:
div {
height: 300px;
background: red;
position: relative;
}
div:before {
content: '';
position: absolute;
top: 0; right: 0;
border-top: 80px solid white;
border-left: 80px solid red;
width: 0;
}
P.S。 The upcoming border-corner-shape
正是您所需要的。太糟糕了,它可能会从规范中删除,并且永远不会进入任何浏览器:(
答案 1 :(得分:43)
如果您需要透明剪切边,则可以使用旋转的伪元素作为div
的背景,并将其定位以剪切所需的角落:
body {
background: url(http://i.imgur.com/k8BtMvj.jpg);
background-size: cover;
}
div {
position: relative;
width: 50%;
margin: 0 auto;
overflow: hidden;
padding: 20px;
text-align: center;
}
div:after {
content: '';
position: absolute;
width: 1100%; height: 1100%;
top: 20px; right: -500%;
background: rgba(255,255,255,.8);
transform-origin: 54% 0;
transform: rotate(45deg);
z-index: -1;
}

<div>
... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>
</div>
&#13;
请注意,此解决方案使用转换,您需要添加所需的供应商前缀。有关详细信息,请参阅canIuse。
要剪切右下角,您可以将伪元素的top,transform和transform-origin属性更改为:
body {
background: url(http://i.imgur.com/k8BtMvj.jpg);
background-size: cover;
}
div {
position: relative;
width: 50%;
margin: 0 auto;
overflow: hidden;
padding: 20px;
text-align: center;
}
div:after {
content: '';
position: absolute;
width: 1100%; height: 1100%;
bottom: 20px; right: -500%;
background: rgba(255,255,255,.8);
transform-origin: 54% 100%;
transform: rotate(-45deg);
z-index: -1;
}
&#13;
<div>
... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>... content ...<br/>
</div>
&#13;
答案 2 :(得分:24)
使用clip-path是一种新的,即将到来的替代方案。它开始得到越来越多的支持,现在已经有了很好的记录。由于它使用SVG来创建形状,因此它可以直接开箱即用。
div {
width: 200px;
min-height: 200px;
-webkit-clip-path: polygon(0 0, 0 100%, 100% 100%, 100% 25%, 75% 0);
clip-path: polygon(0 0, 0 100%, 100% 100%, 100% 25%, 75% 0);
background: lightblue;
}
&#13;
<div>
<p>Some Text</p>
</div>
&#13;
我有替代web-tiki的转换答案。
body {
background: lightgreen;
}
div {
width: 200px;
height: 200px;
background: transparent;
position: relative;
overflow: hidden;
}
div.bg {
width: 200%;
height: 200%;
background: lightblue;
position: absolute;
top: 0;
left: -75%;
transform-origin: 50% 50%;
transform: rotate(45deg);
z-index: -1;
}
&#13;
<div>
<div class="bg"></div>
<p>Some Text</p>
</div>
&#13;
答案 3 :(得分:13)
您可以使用linear-gradient
。让我们说父母div
有一张背景图片,你需要一个div
坐在上面,灰色背景和狗耳左角。你可以这样做:
.parent-div { background: url('/image.jpg'); }
.child-div {
background: #333;
background: linear-gradient(135deg, transparent 30px, #333 0);
}
进一步阅读:
答案 4 :(得分:13)
这是使用CSS transform: skew(45deg)
生成切角效果的另一种方法。形状本身包含三个元素(1个真元素和2个伪元素),如下所示:
div
元素具有overflow: hidden
并生成左边框。:before
伪元素,它是父容器高度的20%,并且应用了倾斜变换。这个元素突出了顶部的边框,并在右侧切割(倾斜)边框。:after
伪元素,它是父级高度的80%(基本上是剩余高度),并产生底部边框,右边框的剩余部分。产生的输出是响应性的,在顶部产生透明切口并支持透明背景。
div {
position: relative;
height: 100px;
width: 200px;
border-left: 2px solid beige;
overflow: hidden;
}
div:after,
div:before {
position: absolute;
content: '';
width: calc(100% - 2px);
left: 0px;
z-index: -1;
}
div:before {
height: 20%;
top: 0px;
border: 2px solid beige;
border-width: 2px 3px 0px 0px;
transform: skew(45deg);
transform-origin: right bottom;
}
div:after {
height: calc(80% - 4px);
bottom: 0px;
border: 2px solid beige;
border-width: 0px 2px 2px 0px;
}
.filled:before, .filled:after {
background-color: beige;
}
/* Just for demo */
div {
float: left;
color: beige;
padding: 10px;
transition: all 1s;
margin: 10px;
}
div:hover {
height: 200px;
width: 300px;
}
div.filled{
color: black;
}
body{
background-image: radial-gradient(circle, #3F9CBA 0%, #153346 100%);
}
&#13;
<div class="cut-corner">Some content</div>
<div class="cut-corner filled">Some content</div>
&#13;
以下是使用linear-gradient
背景图像生成切角效果的另一种方法。使用3个梯度图像(下面给出)的组合:
产生的输出是响应性的,产生透明切割并且不需要任何额外的元素(真实的或伪的)。缺点是这种方法只有在背景(填充)是纯色并且很难产生边框时才有效(但仍然可以在片段中看到)。
.cut-corner {
height: 100px;
width: 200px;
background-image: linear-gradient(to bottom left, transparent 50%, beige 50%), linear-gradient(beige, beige), linear-gradient(beige, beige);
background-size: 25px 25px, 100% 100%, 100% 100%;
background-position: 100% 0%, -25px 0%, 100% 25px;
background-repeat: no-repeat;
}
.filled {
background-image: linear-gradient(black, black), linear-gradient(black, black), linear-gradient(black, black), linear-gradient(black, black), linear-gradient(to bottom left, transparent calc(50% - 1px), black calc(50% - 1px), black calc(50% + 1px), beige calc(50% + 1px)), linear-gradient(beige, beige), linear-gradient(beige, beige);
background-size: 2px 100%, 2px 100%, 100% 2px, 100% 2px, 25px 25px, 100% 100%, 100% 100%;
background-position: 0% 0%, 100% 25px, -25px 0%, 0px 100%, 100% 0%, -25px 0%, 100% 25px;
}
/* Just for demo */
*{
box-sizing: border-box;
}
div {
float: left;
color: black;
padding: 10px;
transition: all 1s;
margin: 10px;
}
div:hover {
height: 200px;
width: 300px;
}
body{
background-image: radial-gradient(circle, #3F9CBA 0%, #153346 100%);
}
&#13;
<div class="cut-corner">Some content</div>
<div class="cut-corner filled">Some content</div>
&#13;
答案 5 :(得分:7)
如果你需要一个对角线边框而不是一个对角线,你可以用每个伪元素叠加2个div:
样本
http://codepen.io/remcokalf/pen/BNxLMJ
<div id="grey"></div>
<div class="container">
<div class="diagonal">
<h2>Header title</h2>
<p>Yes a CSS diagonal corner is possible</p>
</div>
<div class="diagonal2">
<h2>Header title</h2>
<p>Yes a CSS diagonal corner with background image is possible</p>
</div>
<div class="diagonal3">
<div class="inside">
<h2>Header title</h2>
<p>Yes a CSS diagonal border is even possible with an extra div</p>
</div>
</div>
</div>
&#13;
<?php
while ( $featured_query->have_posts() ) :
$featured_query->the_post();
$post_id = get_the_ID();
$slide_more_link = get_post_meta( $post_id, '_et_slide_more_link', true );
$more_link = '' != $slide_more_link ? $slide_more_link : get_permalink();
$class = 'et-first';
$truncate_length = 610;
$width = (int) apply_filters( 'et_slider_image_width', 578 );
$height = (int) apply_filters( 'et_slider_image_height', 420 );
$title = get_the_title();
if ( 2 === $i ) {
$class = 'et-second';
$truncate_length = 250;
$width = (int) apply_filters( 'et_slider_image_medium_width', 578 );
$height = (int) apply_filters( 'et_slider_image_medium_height', 208 );
} else if ( 1 !== $i ) {
$class = 3 === $i ? 'et-third' : 'et-fourth';
$truncate_length = 75;
$width = (int) apply_filters( 'et_slider_image_small_width', 287 );
$height = (int) apply_filters( 'et_slider_image_small_height', 208 );
}
if ( is_category() ) {
$truncate_length = 390;
$width = (int) apply_filters( 'et_slider_category_image_width', 578 );
$height = (int) apply_filters( 'et_slider_category_image_height', 280 );
}
$thumbnail = get_thumbnail( $width, $height, '', $title, $title, false, 'Featured' );
$thumb = $thumbnail["thumb"];
?>
&#13;
答案 6 :(得分:5)
此代码允许您在矩形的每一边切角:
div {
display:block;
height: 300px;
width: 200px;
background: url('http://lorempixel.com/180/290/') no-repeat;
background-size:cover;
-webkit-clip-path: polygon(10px 0%, calc(100% - 10px) 0%, 100% 10px, 100% calc(100% - 10px), calc(100% - 10px) 100%, 10px 100%, 0% calc(100% - 10px), 0% 10px);
clip-path: polygon(10px 0%, calc(100% - 10px) 0%, 100% 10px, 100% calc(100% - 10px), calc(100% - 10px) 100%, 10px 100%, 0% calc(100% - 10px), 0% 10px);
}
答案 7 :(得分:3)
对Joseph的代码进行少量编辑后,该元素不需要可靠的背景:
div {
height: 300px;
background: url('http://images2.layoutsparks.com/1/190037/serene-nature-scenery-blue.jpg');
position: relative;
}
div:before {
content: '';
position: absolute;
top: 0; right: 0;
border-top: 80px solid white;
border-left: 80px solid rgba(0,0,0,0);
width: 0;
}
http://jsfiddle.net/2bZAW/1921/
使用' rgba(0,0,0,0)'可以使内部'角落'不可见
您还可以编辑第4个参数'a',其中 0&lt; a&lt; 1 ,为更多的“折角”效果留下阴影:
http://jsfiddle.net/2bZAW/1922/(有阴影)
注意: IE9 +,Firefox 3 +,Chrome,Safari和Opera 10 +支持RGBA颜色值。
答案 8 :(得分:2)
我们的切割元素存在不同背景颜色的问题。我们只想要右上角和左下角。
body {
background-color: rgba(0,0,0,0.3)
}
.box {
position: relative;
display: block;
background: blue;
text-align: center;
color: white;
padding: 15px;
margin: 50px;
}
.box:before,
.box:after {
content: "";
position: absolute;
left: 0;
right: 0;
bottom: 100%;
border-bottom: 15px solid blue;
border-left: 15px solid transparent;
border-right: 15px solid transparent;
}
.box:before{
border-left: 15px solid blue;
}
.box:after{
border-right: 15px solid blue;
}
.box:after {
bottom: auto;
top: 100%;
border-bottom: none;
border-top: 15px solid blue;
}
/* Active box */
.box.active{
background: white;
color: black;
}
.active:before,
.active:after {
border-bottom: 15px solid white;
}
.active:before{
border-left: 15px solid white;
}
.active:after{
border-right: 15px solid white;
}
.active:after {
border-bottom: none;
border-top: 15px solid white;
}
&#13;
<div class="box">
Some text goes here. Some text goes here. Some text goes here. Some text goes here.<br/>Some text goes here.<br/>Some text goes here.<br/>Some text goes here.<br/>Some text goes here.<br/>Some text goes here.<br/>
</div>
<div class="box">
Some text goes here.
</div>
<div class="box active">
Some text goes here.
<span class="border-bottom"></span>
</div>
<div class="box">
Some text goes here.
</div>
&#13;
答案 9 :(得分:2)
另一个想法是使用掩码和 CSS 变量来更好地控制整个形状。它具有响应性、透明性并允许任何类型的背景:
.box {
--all:0px;
width:200px;
height:150px;
display:inline-block;
margin:10px;
background:red;
-webkit-mask:
linear-gradient( 45deg, transparent 0 var(--bottom-left,var(--all)) ,#fff 0) bottom left,
linear-gradient( -45deg, transparent 0 var(--bottom-right,var(--all)),#fff 0) bottom right,
linear-gradient( 135deg, transparent 0 var(--top-left,var(--all)) ,#fff 0) top left,
linear-gradient(-135deg, transparent 0 var(--top-right,var(--all)) ,#fff 0) top right;
-webkit-mask-size:50.5% 50.5%;
-webkit-mask-repeat:no-repeat;
}
body {
background:grey;
}
<div class="box" style="--top-left:20px"></div>
<div class="box" style="--top-right:20px;--bottom-right:50px;background:radial-gradient(red,yellow)"></div>
<div class="box" style="--all:30px;background:url(https://picsum.photos/id/104/200/200)"></div>
<div class="box" style="--all:30px;--bottom-right:0px;background:linear-gradient(red,blue)"></div>
<div class="box" style="--all:50%;width:150px;background:green"></div>
<div class="box" style="--all:12%;width:150px;background:repeating-linear-gradient(45deg,#000 0 10px,#fff 0 20px)"></div>
如果您想考虑边框,则在下面:
.box {
--all:0px;
--b:pink;
width:200px;
height:150px;
display:inline-block;
margin:10px;
border:5px solid var(--b);
background:
linear-gradient( 45deg, var(--b) 0 calc(var(--bottom-left,var(--all)) + 5px) ,transparent 0) bottom left /50% 50%,
linear-gradient( -45deg, var(--b) 0 calc(var(--bottom-right,var(--all)) + 5px),transparent 0) bottom right/50% 50%,
linear-gradient( 135deg, var(--b) 0 calc(var(--top-left,var(--all)) + 5px) ,transparent 0) top left /50% 50%,
linear-gradient(-135deg, var(--b) 0 calc(var(--top-right,var(--all)) + 5px) ,transparent 0) top right /50% 50%,
var(--img,red);
background-origin:border-box;
background-repeat:no-repeat;
-webkit-mask:
linear-gradient( 45deg, transparent 0 var(--bottom-left,var(--all)) ,#fff 0) bottom left,
linear-gradient( -45deg, transparent 0 var(--bottom-right,var(--all)),#fff 0) bottom right,
linear-gradient( 135deg, transparent 0 var(--top-left,var(--all)) ,#fff 0) top left,
linear-gradient(-135deg, transparent 0 var(--top-right,var(--all)) ,#fff 0) top right;
-webkit-mask-size:50.5% 50.5%;
-webkit-mask-repeat:no-repeat;
}
body {
background:grey;
}
<div class="box" style="--top-left:20px"></div>
<div class="box" style="--top-right:20px;--bottom-right:50px;--img:radial-gradient(red,yellow);--b:white;"></div>
<div class="box" style="--all:30px;--img:url(https://picsum.photos/id/104/200/200) center/cover;--b:orange;"></div>
<div class="box" style="--all:30px;--bottom-right:0px;--img:linear-gradient(red,blue)"></div>
<div class="box" style="--all:50%;width:150px;--img:green;--b:red;"></div>
<div class="box" style="--all:12%;width:150px;--img:repeating-linear-gradient(45deg,#000 0 10px,#fff 0 20px)"></div>
让我们也添加一些半径:
.box {
--all:0px;
--b:pink;
width:200px;
height:150px;
display:inline-block;
margin:10px;
filter:url(#round);
}
.box::before {
content:"";
position:absolute;
top:0;
left:0;
right:0;
bottom:0;
background:var(--img,red);
-webkit-mask:
linear-gradient( 45deg, transparent 0 var(--bottom-left,var(--all)) ,#fff 0) bottom left,
linear-gradient( -45deg, transparent 0 var(--bottom-right,var(--all)),#fff 0) bottom right,
linear-gradient( 135deg, transparent 0 var(--top-left,var(--all)) ,#fff 0) top left,
linear-gradient(-135deg, transparent 0 var(--top-right,var(--all)) ,#fff 0) top right;
-webkit-mask-size:50.5% 50.5%;
-webkit-mask-repeat:no-repeat;
}
body {
background:grey;
}
<div class="box" style="--top-left:20px"></div>
<div class="box" style="--top-right:20px;--bottom-right:50px;--img:radial-gradient(red,yellow);--b:white;"></div>
<div class="box" style="--all:30px;--img:url(https://picsum.photos/id/104/200/200) center/cover;--b:orange;"></div>
<div class="box" style="--all:30px;--bottom-right:0px;--img:linear-gradient(red,blue)"></div>
<div class="box" style="--all:50%;width:150px;--img:green;--b:red;"></div>
<div class="box" style="--all:12%;width:150px;--img:repeating-linear-gradient(45deg,#000 0 10px,#fff 0 20px)"></div>
<svg style="visibility: hidden; position: absolute;" width="0" height="0" xmlns="http://www.w3.org/2000/svg" version="1.1">
<defs>
<filter id="round">
<feGaussianBlur in="SourceGraphic" stdDeviation="5" result="blur" />
<feColorMatrix in="blur" mode="matrix" values="1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 19 -9" result="goo" />
<feComposite in="SourceGraphic" in2="goo" operator="atop"/>
</filter>
</defs>
</svg>
答案 10 :(得分:1)
根据哈利的线性梯度解决方案(10月14日和9月15日15:55回答),它表示不透明背景是不可能的,我试过它,是的,它不是&# 39;吨。
但是!我找到了一个解决方法。不,它没有超级优化,但它有效。所以这是我的解决方案。由于Harry不使用伪元素,我们可以通过创建一个来实现。
设置相对于容器的位置,并创建具有相同线性渐变属性的伪元素。换句话说,只需克隆它。然后为容器放置透明背景,并为克隆说一个黑色背景。将绝对位置放在上面,z指数为-1,不透明度值(即50%)。它会完成这项工作。再次,这是一个解决方法,它并不完美,但它的工作正常。
.cut-corner {
position: relative;
color: white;
background-repeat: no-repeat;
background-image: linear-gradient(white, white), linear-gradient(white, white), linear-gradient(white, white), linear-gradient(white, white), linear-gradient(to bottom left, transparent calc(50% - 1px), white calc(50% - 1px), white calc(50% + 1px), transparent calc(50% + 1px)), linear-gradient(transparent, transparent), linear-gradient(transparent, transparent);
background-size: 2px 100%, 2px 100%, 100% 2px, 100% 2px, 25px 25px, 100% 100%, 100% 100%;
background-position: 0% 0%, 100% 25px, -25px 0%, 0px 100%, 100% 0%, -25px 0%, 100% 25px;
}
.cut-corner:after {
content: "";
position: absolute;
left: 0;
bottom: 0;
right: 0;
top: 0;
z-index: -1;
opacity: 0.5;
background-repeat: no-repeat;
background-image: linear-gradient(white, white), linear-gradient(white, white), linear-gradient(white, white), linear-gradient(white, white), linear-gradient(to bottom left, transparent calc(50% - 1px), white calc(50% - 1px), white calc(50% + 1px), black calc(50% + 1px)), linear-gradient(black, black), linear-gradient(black, black);
background-size: 2px 100%, 2px 100%, 100% 2px, 100% 2px, 25px 25px, 100% 100%, 100% 100%;
background-position: 0% 0%, 100% 25px, -25px 0%, 0px 100%, 100% 0%, -25px 0%, 100% 25px;
}
/* Just for demo */
div {
padding: 10px;
}
body{
background-image: radial-gradient(circle, #3F9CBA 0%, #153346 100%);
}
&#13;
<div class="cut-corner">
Some content<br>
Some content<br>
Some content<br>
Some content
</div>
&#13;
答案 11 :(得分:1)
您可以使用clip-path
,如Stewartside和Sviatoslav Oleksiv所述。为了简单起见,我创建了一个Sass mixin:
@mixin cut-corners ($left-top, $right-top: 0px, $right-bottom: 0px, $left-bottom: 0px) {
clip-path: polygon($left-top 0%, calc(100% - #{$right-top}) 0%, 100% $right-top, 100% calc(100% - #{$right-bottom}), calc(100% - #{$right-bottom}) 100%, $left-bottom 100%, 0% calc(100% - #{$left-bottom}), 0% $left-top);
}
.cut-corners {
@include cut-corners(10px, 0, 25px, 50px);
}
答案 12 :(得分:0)
通过对Joshep代码的小修改...您可以使用此代码,根据您的要求,似乎右下角向下折叠。
div {
height: 300px;
background: red;
position: relative;
}
div:before {
content: '';
position: absolute;
top: 0; right: 0;
border-top: 80px solid white;
border-left: 80px solid blue;
width: 0;
}
答案 13 :(得分:0)
我最近切断了右上角并将文件夹覆盖在文件夹上。完整的代码noob,所以忽略糟糕的代码,但我通过组合一个正方形,一个三角形和一个矩形来做到这一点...这可能是也可能不是一种新的方法,但希望有人觉得它很有帮助。
https://i.stack.imgur.com/qFMRz.png
这是HTML:
<!DOCTYPE html>
<html lang ="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" type="text/css" href="style.css">
</head>
<body>
<div class="folders">
<div class="container">
<div class="triangleOne">
<p class="folderNames">Home</p>
</div>
<div class="triangleOneCut">
</div>
<div class="triangleOneFill">
</div>
</div>
<div class="container2">
<div class="triangleOne blue">
<p class="folderNames">About</p>
</div>
<div class="triangleOneCut blueCut">
</div>
<div class="triangleOneFill blue">
</div>
</div>
<div class="container3">
<div class="triangleOne green">
<p class="folderNames">Contact</p>
</div>
<div class="triangleOneCut greenCut">
</div>
<div class="triangleOneFill green">
</div>
</div>
</div>
</body>
</html>
这是CSS:
.triangleOne {
height: 50px;
width: 40px;
background: red;
border-radius: 5px 0px 0px 5px;
position: absolute;
}
.triangleOneCut {
content: '';
position: absolute;
top: 0; left: 40px;
border-top: 10px solid transparent;
border-left: 10px solid red;
width: 0;
}
.triangleOneFill {
content: '';
position: absolute;
top: 10px; left: 40px;
width: 10px;
height: 40px;
background-color: red;
border-radius: 0px 0px 5px 0px;
}
.container {
position: relative;
height: 50px;
width: 50px;
display: inline-block;
z-index: 3;
}
.container2 {
position: relative;
height: 50px;
width: 50px;
display: inline-block;
left: -10px;
z-index: 2;
}
.container3 {
position: relative;
height: 50px;
width: 50px;
display: inline-block;
left: -20px;
z-index: 1;
}
.blue {
background-color: blue;
}
.green {
background-color: green;
}
.blueCut {
border-left: 10px solid blue;
}
.greenCut {
border-left: 10px solid green;
}
.folders {
width: 160px;
height: 50px;
/* border: 10px solid white; */
margin: auto;
padding-left: 25px;
margin-top: 100px;
}
.folderNames {
text-align: right;
padding-left: 2px;
color: white;
margin-top: 1.5px;
font-family: monospace;
font-size: 6.5px;
border-bottom: double 1.5px white;
}
答案 14 :(得分:0)
另一种解决方案: html:
<div class="background">
<div class="container">Hello world!</div>
</div>
css:
.background {
position: relative;
width: 50px;
height: 50px;
border-right: 150px solid lightgreen;
border-bottom: 150px solid lightgreen;
border-radius: 10px;
}
.background::before {
content: "";
position: absolute;
top: 0;
left: 0;
width: 0;
height: 0;
border: 25px solid lightgreen;
border-top-color: transparent;
border-left-color: transparent;
}
.container {
position: absolute;
padding-left: 25px;
padding-top: 25px;
font-size: 38px;
font-weight: bolder;
}
答案 15 :(得分:0)
如果您不希望使用纯色背景(即仅带有方形角的边框),这是一个解决方案。
.container {
width: 100px;
height: 100px;
background-color: white;
border: 1px solid black;
position: relative;
}
.border {
position: absolute;
width: 100%;
height: 100%;
}
.border:before {
content: '';
position: absolute;
border-top: 15px solid white;
border-left: 15px solid white;
width: 0;
}
.border:after {
content: '';
position: absolute;
width: 16px;
height: 1px;
background: black;
}
.tl:before { top: -5px; left: -5px; transform: rotate(-45deg); }
.tl:after { top: 5px; left: -3px; transform: rotate(-45deg);}
.tr:before { top: -5px; right: -5px; transform: rotate(45deg); }
.tr:after { top: 5px; right: -3px; transform: rotate(45deg); }
.bl:before { bottom: -5px; left: -5px; transform: rotate(45deg); }
.bl:after { bottom: 5px; left: -3px; transform: rotate(45deg); }
.br:before { bottom: -5px; right: -5px; transform: rotate(-45deg); }
.br:after { bottom: 5px; right: -3px; transform: rotate(-45deg); }
<html>
<body>
<div class="container">
<div class="border tl"></div>
<div class="border tr"></div>
<div class="border bl"></div>
<div class="border br"></div>
</div>
</body>
</html>